Study On The Coding-decoding Of Turbo-code And Its Application In 3G

Coding is an important method approaching to Shannon-limit performance. Since information theory was established fifty years ago, coding has got much substantial progress in theory and technology. Now error-correcting coding technology is essential for all communication systems. The coding scheme that has simple structure and superior performance is the goal which communication work always goes in for. It is also hoped to satisfy the need of communication services. Turbo-code is the most successful.Turbo-code is a new class of coding schemes, which was first introduced by Claude Berrou in 1993. The principal characteristics of Turbo-code are that two or two more encoders separated by an random interleaver are used in coding part, and the iterative feedback decoding algorithms based on soft input/output are used in decoding part. The interleaver endows the code word with approximate random characteristic and the cascade connection make the code word longer. Two procedures are accessible that the method of maximum a posteriori estimation and the iterative feedback algorithms are used in the decoders, and the maximum likelihood algorithm is used in the decoders. Turbo-code gains the superior performance that nearly approaches Shannon-limit because it makes use of the three conditions in Shannon theory.Turbo-code has been arresting zealous researches from the academia of coding and informatics area since 1993. It is for its outstanding performance that Turbo-code has been widely used in telecommunications and has been selected as one of the coding schemes in the third generation (3G) communication systems. In the 3G systems, WCDMA, CDMA2000 and TD-SCDMA all use Turbo-code as their coding scheme for high speed and high quality services. This paper analyses the system performances as Turbo-code is used in the 3G systems by computer simulation under the background of application. To sum up, the main conclusion and production as follows:1. In this paper, the history, sort, development and future of channel-code and Turbo-code are reviewed. The status and application area of Turbo-code are also mentioned. This paper recommends the code-decode structure and basic principle of Turbo-code in detail. As a consequence we can know that Turbo-code has excellent advantages and can provide near Shannon-limit coding performance. Firstly, each component of the code structure is discussed in detail, such as recursive systematic convolutional (RSC), interleaver, puncturing matrix and so on.In which we give an account of all kinds of interleavers according to classification because of the importance. Next, the architecture of the Turbo decoder and the principle based on the soft judgment are discussed. All of the contents settle the theoretic basic for the next research.2. In the paper, two kinds of decoding algorithms are compared. One is the method of maximum a posteriori algorithm (MAP) and the other is the Soft-Output Viterbi algorithm. We mainly focus on the derivation of the MAP algorithm and from which we can get some reduction algorithm, such as Log-MAP, MAX-Log-MAP etc. Some decoding algorithms of Turbo-code in common use are compared in their capability and complexity.Firstly, according to the basic flow chart of code-decode, the main conclusions can be got from computer simulations: difference exits between these decoding algorithms and each one has its own advantage and disadvantage. The Log-MAP and MAX-Log-MAP algorithms are of more applicable on the premise of lowing the complexity, considering the balance between performance and real-time.Secondly, besides the decoding algorithms, there are also some factors that can affect the performance of Turbo-code, such as different encoders, the iterative decoding times, the design of interleavers, the rate etc. By programming emulation, this paper analyzes the parameters influence on the performance of the Turbo Code using the Log-MAP algorithm. The conclusion is that Turbo-code has good performance in low SNR over AWGN channel. We can also know that lowing the coding rate, increasing the length of interleaver, the constraint length and the iterative decoding times can improve the performance of Turbo-code.3. The structure of channel-code and parameter of standard in the 3G systems are designed in this paper. A new 3GPP standard interleaver is studied in detail and the performance of Turbo-code using this interleaver is analyzed by computer simulation.Firstly, the design principle of this 3GPP standard interleaver is described in detail. Next, the performance of Turbo-code using the 3GPP standard interleaver is compared with those using some other interleavers. By computer simulation we can get the conclusion that the performance of Turbo-code using the 3GPP standard interleaver has better performance which can satisfy the requirement of the bit-error rate (BER) and real-time in the 3G system. The bit-error performance can achieve a BER of 10?6 with BPSK modulation, an input frame size of 1024 bits, a generator matrix of G =(1 3,11), a rate of 1/3, three iterative decoding times, and using MAX-Log-MAP algorithm in low SNR over AWGN channel.Additionally, the coding channel model over Rayleigh is addressed and the performance of Turbo-code over Rayleigh channel is given by computer simulation against the fading in wireless channel. The conclusion is that Turbo-code over Rayleigh channel can also have good performance although it is worse than the performance over AWGN channel. The result of simulation indicates that Turbo-code can well resist fading and multipath effect, which can help us to choose the parameter of Turbo-code to improve its capability over wireless channel.Not only is the significance of Turbo-code that its performances approach to Shannon limit, but also its principle of coding and method of achievement show a way to code-decode theory. Some new codes are researched such as LDPC and asymmetric Turbo-code etc. Besides the important academic and theoretical meaning, Turbo-code has great application background and practical value. People begin to apply the principle of Turbo-code to many aspects such as demodulation /decode, multi-user detection, synchronization and channel estimation etc. It can be believed that Turbo-code will be applied more and more widely in the field of communication and the digital electronic technique along with further research, further improvement on interleaver and decoding algorithm, further advancement of calculating speed.